1. Field of the Invention
This invention relates to a rotation shaft seal, especially, a rotation shaft seal used for sealing high pressure fluid in a compressor for an air conditioner on an automobile.
2. Description of the Related Art
As a conventional rotation shaft seal of this kind, a shaft seal as shown in FIG. 41 is known. This rotation shaft seal is disposed between a housing 31 such as a case of a compressor and a rotation shaft 32 for sealing fluid or gas in a fluid storing chamber 33.
In the construction of the shaft seal, a seal member 35 made of rubber is adhered to an outer case 34, and a first seal element 36 and a second seal element 37 made of synthetic resin (such as PTFE) having spiral grooves are unified with a first inner case 38, a washer 39, a second inner case 40, etc. in the outer case 34 (by caulking).
The seal member 35 made of rubber is provided with a lip portion 42 protruding to the fluid storing chamber 33 side, the lip portion 42 has a concave portion 44 in a peripheral direction on the fluid storing chamber 33 side and a lip end portion 41 gradually diminishes in diameter to the fluid storing chamber 33 side, and, a tip of the lip end portion 41 contacts the rotation shaft 32 as to make a belt contact area to seal. That is to say, when the shaft is still, fluid is completely sealed by pressure of the fluid storing chamber 33 and elastic force of the lip end portion 41 itself.
And, when the rotation shaft 32 rotates, although slight leakage is generated in a sliding portion of the lip end portion 41 and the rotation shaft 32, the leakage is pushed back (to the left side in FIG. 41) by hydrodynamic effect of the spiral grooves (screw threads) of the first seal element 36 and the second seal element 37. The construction can seal the fluid as a whole.
To describe concretely, as shown in FIG. 42A, in the seal member 35 made of rubber in a non-attached state to the rotation shaft 32 (free state), an interference G is arranged on the lip end portion 41 to form an interference portion 46 inner to the periphery of the rotation shaft 32. And, as shown in FIG. 42B, in the seal member 35 attached to the rotation shaft 32, tightening force F11 generated by elasticity of rubber works on a contact portion 43 (with the rotation shaft 32) of the lip end portion 41 (the interference portion 46) to a peripheral face of the rotation shaft 32. And, as shown in FIG. 42C, in the seal member 35 pressurized (by pressure P of the fluid) in a pressurizing state of the fluid storing chamber 33, self-sealing force F12 (generated by pressurization) and the tightening force F11 (working continuously) work on the contact portion 43. Consequently, total force F15 (=F11+F12) works on the contact portion 43 to the peripheral face of the rotation shaft 32.
In the conventional seal described above, in case that the pressure in the fluid storing chamber 33 is high, the lip end portion 41 contacts the rotation shaft 32 with a large area for great deformation (by high pressure working in an arrow P direction in FIG. 42C), sealability becomes unstable, and sealability of the first seal element 36 is also influenced. This causes problems that leakage is generated early, and abrasion of the contact portion of the lip end portion 41 with the rotation shaft 32 is large.
Further, root of the lip portion 42 has larger pressure receiving area and smaller amount of rubber (in comparison with other parts of the lip portion 42) for the concave portion 44. Therefore, fissures on the root of the lip portion 42 and exfoliation of the seal member 35 from the outer case 34 are generated because the root of the lip portion 42 is greatly deformed by the high pressure and stress is successively generated from the surface of the lip portion 42 to the outer case 34. Further, there is a problem that the contact portion of the lip end portion 41 with the rotation shaft 32 becomes larger, and lifetime of the seal is shortened.
Further, in case that carbon dioxide, having high permeability against rubber and resin, is used as a cooling medium, carbon dioxide permeates the seal member 35 made of rubber, the first seal element 36, and the second seal element 37 and leaks from the seal. That is to say, when leakage of the cooling medium is large, the cooling medium becomes short early, and inconvenience such as reduction of cooling effect for shortage of cooling medium is caused thereby.
It is therefore an object of the present invention to provide a rotation shaft seal used especially under high pressure (around 3 to 10 MPa, for use of high pressure cooling media such as CO2), with which leakage of the cooling medium is restricted, deformation of the lip end portion is small, the lip end portion has good durability for prevention of early abrasion, and sealability is stable with the contact area prevented from being enlarged.